To meet the demand for higher integration density and operating speed of LSIs, the effort to reduce the pattern rule is in rapid progress. The wide-spreading flash memory market and the demand for increased storage capacities drive forward the miniaturization technology. As the advanced miniaturization technology, a self-aligned double patterning (SADP) process involving the steps of forming a resist pattern by ArF lithography, growing a film on opposite sides of pattern features, and forming two pattern features with a half line width from one resist pattern feature is utilized to manufacture 20-nm node devices on a mass scale. One candidate for the microprocessing technology for manufacturing 10-nm node devices of the next generation is a self-aligned quadruple patterning (SAQP) process involving repeating twice the SADP process of ArF lithography patterning. However, the SAQP process is believed very expensive in that formation of sidewall film by CVD and subsequent processing by dry etching must be repeated many times. The EUV lithography of wavelength 13.5 nm is capable of forming a pattern with a 10-nm size via a single exposure step, but suffers from low productivity because the laser power is yet low. As a way out of the deadlock of the miniaturization technology, the development of 3D devices such as vertically stacked flash memories typically BiCS is in progress, but this process is also expensive.
As compared with the line pattern, the hole pattern is difficult to reduce the feature size. The SADP process is applicable to the line pattern to reduce its pitch to half, but not applicable to the hole pattern which is a two-dimensional pattern. Rather than the method of forming a hole pattern by combining a dark-field mask with a positive resist material, the method of forming a hole pattern by combining a bright-field mask of dot pattern with a negative resist material is successful in forming a finer hole pattern because of a higher optical contrast. If a negative resist material improved enough to surpass the resolution of positive resist material is developed, it will become possible to form a fine hole pattern by combining it with the dot pattern mask.
Recently a highlight is put on the organic solvent development again. A positive resist composition featuring a high resolution is subjected to organic solvent development to form a negative pattern. As the ArF resist composition for negative tone development with organic solvent, positive ArF resist compositions of the prior art design may be used. Such pattern forming process is described in Patent Document 1.
In forming a negative pattern of resist film, a bright-field pattern like a dot pattern is necessary at the mask pattern forming stage. In this case, the negative resist material has such advantages as a high throughput and minimized impact of backscattering on account of a reduced image area over the positive resist material. There is a need for a negative resist material having improved resolution.
The resist material for mask pattern formation must have dry etch resistance because the underlying is a metal film which is difficult to process such as Cr or MoSi. In the above-mentioned method of forming a negative pattern via organic solvent development of ArF resist composition, dry etch resistance is short because cyclic protective groups having dry etch resistance have been eliminated from the film that is left as the negative pattern. Thus, the method of forming a negative pattern via organic solvent development of resist film after deprotection is not viable.
Negative resist material of crosslink type suffers bridging between pattern features and pattern collapse due to swelling. A study is thus made on negative resist material of polarity change type rather than the crosslink type. Patent Document 2 discloses a negative resist composition utilizing the polarity change reaction that a hydroxycarboxylic structure cyclizes to form a lactone structure. Patent Document 3 describes a negative resist composition of polarity change type utilizing pinacol-pinacolone rearrangement.
For the purpose of improving etch resistance, on the other hand, styrene copolymers were first proposed. Later proposed are indene copolymers and acenaphthylene copolymers as described in Patent Documents 4 and 5. These copolymers intend to improve etch resistance by utilizing a high carbon density and a robust backbone framework of cycloolefin structure.